1. Field of the Invention
This invention relates generally to commercial mushroom production, and more particularly to the stimulation of mushroom growth by the supplementation of nutrients which are directly utilized by the mushroom.
2. Description of Prior Art
Commercial mushroom growing depends on composted materials as a medium for growth. A compost is first formed and is treated so that the microorganisms present are stimulated to make the compost suitable for colonization by the mushroom.
It has heretofore been known to supplement the compost with various additives including dried blood, cottonseed meal, and many other supplements. These supplements, however, have been added for the purpose of feeding the microorganism population of the compost in order to more actively transform the compost material into a food source for the mushroom mycelium. Little, if any, of the supplements used in the prior art remain available to stimulate mushroom growth directly. The tremendous increase in heat evolution when readily available foods are added to a compost is evidence for this conversion and relatively complete utilization.
It was reported by Schisler et al, Mushroom Science V, pages 150-164 (1962), and Sinden et al, Mushroom Science V, pages 267-280 (1962) that attempts at directly feeding the mycelium rather than indirectly as in the past, were successful and produced marked stimulation of mushroom crop yields, when certain uncomposted nutrients were added to the compost at the time the mushroom mycelium is spawned into the compost, or at the time of casing, i.e., the covering of the compost with a layer of topsoil or peat, through which the developing mycelium grows and on which the mushrooms form.
However, while a significant 10% crop increase was found when small amounts of these supplements were added at spawning, higher rates of supplementation did not further increase the yield. This limited effect seems to be attributed to the fact that the addition of the uncomposted supplements not only stimulated the mycelial growth of the mushroom, but also promoted the growth of the competing microorganisms present in the compost, which tended to reduce the availability of the added nutrients for the mushroom mycelium, and tended to hinder the development of the slower growing mushroom mycelium.
The addition of nutrients which could be utilized directly by the mushroom mycelium, seemed to also present other problems. For one, since the use of direct utilizable nutrients also resulted in an intense stimulation of microbial activity, a very significant temperature increase in the spawned compost occurred, which endangered or destroyed the mushroom mycelium.
Another difficulty with the use of direct utilizable nutrients was that the stimulated crop yields occurred only in the first few flushes. Mushrooms are grown in a series of flushes, or harvests. A single spawning into a compost may produce 5 to 8 flushes, and in some instances as many as 12, or as few as 4 flushes. The remaining compost is then discarded. When the direct utilizable nutrients were added, a significant yield increase was observed in the early flushes, but the nutrients seemed to be rapidly depleted so that little or no yield stimulation was observed in later flushes.
In general, it was found that supplementation of the compost with the direct utilizable nutrients after the mushroom mycelium had become established, such as just before casing, was much more successful, and increased yields were observed which were roughly proportioned to the quantity of nutrients added. This improvement seems to occur because once the mushroom mycelium has begun to develop, its inherent antibiotic activity tends to reduce the competing microorganism population so that only the mycelium obtain the nutrient stimulation.
Therefore, while it would appear most desirable to introduce the nutrients into the compost after the mushroom mycelium has already become well established, such as at the time of casing, certain other practical factors mitigate against supplementation of that stage. One problem is that the increased metabolic rates of the mushroom mycelium can be so severe in the latter stages as to destroy the crop, which again acts as a limiting factor on the quantity of nutrients which could be added.
Unless the mushroom mycelium has become uniformly established throughout the compost, the addition of the supplement could result in spawning the growth of harmful competing molds in those areas of low mycelium colonization.
Another difficulty with supplementation at the time of casing, is that it would require major changes in commercial production techniques. Once the mushroom mycelium has become established, the compost becomes intricately matted together. In order to obtain a uniform distribution of the nutrient throughout the compost, it is necessary to separate the compost using rather sophisticated mechanization.
A still further difficulty of supplementation at the time of casing is that pathogens which are not destroyed by the mushroom mycelium, are more likely to be present at the time of casing than at the time of spawning Usually the compost is pasteurized just before spawning, but pathogen growth may occur unhindered thereafter. Mixing the nutrients into the separated compost at the time of casing could thus result in spreading the pathogens throughout the compost.
The current state of the technology is, therefore, that it is known that nutrients which are directly utilizable by the mushroom mycelium will stimulate growth and increase yield. However, if the nutrients are admixed into the compost before spawning of the mycelium, the practical aspects of mixing are commercially feasible, but the extent of crop stimulation is necessarily limited by the amount of heat evolution, degree of stimulation of competing microorganisms and by the fact that the stimulation of mushroom growth seems to be restricted primarily to the first several flushes. On the other hand, supplementation of the compost at the time of casing seems to result in excellent increases in crop yield, however, the degree of heat evolution caused by the increased metabolic rates of the mushroom mycelium, the practical difficulties in mixing, the danger of the spread of pathogens or the stimulation of competing molds in areas of poor mycelium colonization renders supplementation at this stage generally impractical for commercial utilization.